Molecular design of cross-linked single-ion polymer electrolytes enabling robust LiF-rich solid electrolyte interface for stable lithium metal batteries.

Solid polymer electrolytes (SPEs) with high ionic conductivity, high lithium-ion transference number (t), and good mechanical properties are highly desired for solid-state lithium metal batteries. However, developing SPEs with both high ionic conductivity and high t remains a challenge. Herein, a novel network structure single-ion polymer electrolyte (SIPU) with high ionic conductivity (0.12 mS cm), t (0.71) and mechanical strength (1.5 MPa) was prepared by UV-initiated free radical polymerization and chemically crosslinking of the functional groups. The characterization and Density functional theory (DFT) calculation demonstrate that the construction of a cross-linked network structure not only endows the electrolytes membranes with improved mechanical strength to inhibit dendrite growth but also facilitates fast dissociation of Li for boosting ionic kinetics. More importantly, a robust LiF-rich Solid Electrolyte Interface (SEI) was formed on the Lithium metal anode, enhancing the cycling performance of batteries. As a result, the Li symmetric cells using the SIPU electrolytes can stably cycle over 2000 h. The Li/SIPU/LiFePO cells deliver excellent cycle performance and maintain stably cycling over 1000 cycles at 0.5C. The Li/SIPU/LiNiCoMnO cells also have excellent cycling and rate performance. Furthermore, the Li/SIPU/LiFePO pouch cells exhibit excellent performance. This work provides valuable insights into the rational design of polymer electrolytes with mechanical and electrochemical stability.